Cerebellum/Basal Ganglia

Question 1

Cerebellum

Answer 1

• plans for coordinated movements, adjusts movements, and non-motor functions
• it does not have direct connection to motor neurons
• after cerebellar damage there is NO muscle paralysis or sensory deficits
• Feedback mechanism: receives info from ongoing movements and makes adjustments (adjustor of movements)
• Feedforward mechanism: predicts consequences of motor commands from past experience (comparer of movements) and depending on match/mismatch re-calibrates for future purposes (calibrator of movements)

Question 2

Flow of information into cerebellum

Answer 2

• receives info from motor planning & execution areas from cerebral cortex
• receives sensory feedback info from somatosensory, vestibular, visual, & auditory receptors

Question 3

Parts of the cerebellum

Answer 3

• Flocculonodular lobe (bottom portion near pons) = vestibulocerebellum
• Vermis and Paravermis (top portion near pons) = Spinocerebellum
• Lateral hemisphere (large portion forming point away from pons) = Cerebrocerebellum

Question 4

Flow of information through the circuitry inside the cerebellum

Answer 4

• all inputs to cerebellum via climbing & mossy fibers
• climbing fibers go to 3 deep cerebellar nuclei & purkinji fibers
• mossy fibers go to granule cells & purkinji cells via parallel fibers
• all output via purkinji cells back to cerebellar nuclei
• out of cerebellum to cerebral cortex/brainstem nuclei

Question 5

Vestibulocerebellum

Answer 5

• receives inputs from vestibular system
• outputs back to vestibular nuclei
• efferents from vestibular nuclei regulate VOR centrally to control eye movements & to control neck/trunk axial muscles to influence postural control
• maintaining VOR and balance are the main functions

Question 6

Spinocerebellum

Answer 6

• helps execute coordinated movements using both feedforward and feedback mechanisms
• inputs from spinal cord via 4 spinocerebellar pathways
• receives sensory inputs from visual, auditory, & vestibular systems
• outputs adjust motor activity by influencing medial tracts (posture/tone) and lateral tracts (fine movements) by sending projections from fastigial and IP nuclei to brainstem nuclei & by influencing cerebral cortex via thalamus indirectly

Question 7

Cerebrocerebellum

Answer 7

• involved in planning for coordinated movements
• uses feedforward mechanism
• connections form a loop between the lateral cerebellar hemisphere & cerebral cortex: cerebro-cerebello-cerebral loop
• receives direct inputs from pontine nuclei & gives off direct outputs to thalamus
• involved with motor & cognitive learning

Question 8

Signs of cerebellar dysfunction

Answer 8

• problems with eye movements: nystagmus
• Disequilibrium: loss of balance
• Uncoordinated movements: dysmetria (over/under shooting a movement), ataxia, dyssynergia (inability/desynchronization of movements)
• unilateral cerebellar lesions cause impairments on the same side of body: spinocerebellar afferents are ipsilateral & cerebellar efferents project to contralateral cerebral cortex

Question 9

Lesions in vestibulocerebellum

Answer 9

• nystagmus
• difficulty maintaining sitting/standing balance (truncal ataxia)

Question 10

Lesions in spiinocerebellum

Answer 10

• limb incoordination (DDK, dysmetria)
• ataxic gait (wide based unsteady gait)
• action/intension tremor
• dysarthria

Question 11

Lesions in cerebrocerebellum

Answer 11

• difficulty in planning complex movements (mostly fine motor)
• difficulty with motor areas for playing instruments, fasten buttons, typing on keyboard
• disruption of timing of joint movements (decomposition of movements - dyssnergia)

Question 12

Parts of the basal ganglia

Answer 12

• 5 nuclei: Caudate, Putamen, Globus Pallidus, Subthalamic nucleus, Substantia nugra
• Striatum = Caudate and Putamen
• C-shaped Caudate wraps around the Thalamus
• Lentiform Nucleus = Putamen and Globus Pallidus
• Substantia nigra = compacta & reticularis
• Globus Pallidus = externus and internus

Question 13

Basal ganglia functions

Answer 13

• plans & executes coordinated motor activity but does NOT have direct connections to motor neurons
• involved in movement control for goal-directed behavior & helps in judging/decision making by taking into account socially appropriate/inappropriate situations & emotions
  -for influencing motor control the basal ganglia regulates the level of inhibition in various motor pathways

Question 14

Basal agnails circuitry

Answer 14

• inputs enter caudate/putamen from cerebral cortex
• outputs exit through Globus Pallidus internus/Substantia nigra to the thalamus
• Loops: goal-directed behavior loop, social behavior loop, emotion loop, oculomotor loop, and motor loop

Question 15

Goal-directed behavior loop

Answer 15

• example: deciding whether to run a yellow light when running late to work
• lesion in bilateral caudate = inattention, distractibility, poor concentration, NO movement disorders

Question 16

Social behavior loop

Answer 16

• example: deciding whether to run a yellow light with grandma sitting beside you
• lesion in bilateral caudate head = prone to frustration, hyper sexual, shoplifting, violent, NO movement disorders

Question 17

Emotional behavior/Limbic circuit loop

Answer 17

• example: involved with emotional & reward/pleasure seeking behavior, links emotions & motor systems
• lesion in ventral striatum = depression, emotional blunting “mask-like” facial expression

Question 18

Oculomotor circuit loop

Answer 18

• example: to decide whether to use fast eye movements (saccades) to direct attention to visual objects of interest
• lesions in basal ganglia can cause impaired saccades

Question 19

Motor circuit loop

Answer 19

• regulates movements by indirectly controlling activity in voluntary muscles, postural muscles, & CPG
• this loop up or down regulates activity in various motor tracts to promote desired movements & inhibit undesired ones

Question 20

Influence of basal ganglia on motor pathways

Answer 20

• output of motor circuits is always inhibitory on the motor pathways
• regulates activity of motor thalamus & some other brainstem motor nuclei by having inhibitory influence
• (1) Motor thalamus –> lateral corticospinal & rubrospinal tracts –> MNs to muscles for voluntary movements
• (2) Pedunculopontine nucleus –> reticulospinal tracts –> MNs to postural & girdle muscles
• (3) Midbrain locomotor region –> reticulospinal tracts –> stepping pattern generators (walking)
• output influences voluntary movements, postural & girdle movements, and gait

Question 21

Go/Direct pathway

Answer 21

• facilitates desired movements by disinhibiting thalamus due to increased inhibitory activity of striatum on Globus Pallidus internus
• substantia nigra has fine tuning effect on striatum
• Globus Pallidus internus has the leash to thalamus activity

Question 22

No-go/Indirect pathway

Answer 22

• suppresses unwanted movements by inhibiting thalamus due to increased inhibitory activity of striatum on Globus Pallidus externus

Question 23

Hyperdirect pathway

Answer 23

• purpose is to inhibit all ongoing movements before initiating voluntary movement
• motor cortex sends strong excitatory inputs to sub thalamic nucleus which excites globs pallid us internus which in turn inhibits thalamus

Question 24

What does normal movement need in the 3 pathways

Answer 24

• needs optimal levels of activity in all 3 pathways to promote desired movements & suppress unwanted movements
• optimization between different pathways brought about by the fine tuning by substantia nigra using dopamine

Question 25

What if tuning starts to malfunction

Answer 25

• If the direct pathway becomes less active - may cause lack/slowness of desired movements, ex: bradykinesia
• If the indirect pathway becomes less active - may cause increase in unwanted movements, ex: dyskinesia, chorea, & ballismus

Question 26

Parkinson’s disease

Answer 26

• bradykinesia
• freezing of gait
• tremor
• rigidity - cogwheel type
• non-motor signs: mask like facial expression, depression, psychosis, or dementia